The present invention relates to a fine particle dispersion and a method of manufacturing the same, particularly, to a fine particle dispersion having the viscosity promptly increased upon application of an electric field, exhibiting an electrorheological effect, i.e., the effect that various colors are developed by coloring materials, and acting as an electrorheological (ER) fluid to allow the dispersion to be used as an operating fluid in, for example, an engine mount, a damper and a valve. Since the fine particle dispersion of the present invention is capable of developing various colors, the dispersion can also be used as a coloring material such as a liquid toner and an ink for an ink jet apparatus. The present invention also relates to a method of manufacturing the particular fine particle dispersion.
In the conventional ER fluid of the fine particle dispersion type, the dispersed fine particles have a specific gravity larger than that of the carrier liquid, leading to a poor dispersion of the fine particles.
Also, since a black material such as a carbon black is dispersed in the carrier liquid, the conventional ER fluid cannot be used as a coloring material.
To overcome these difficulties, proposed is an electrorheological (ER) fluid using resin particles having a specific gravity close to that of the carrier liquid. However, the resin particles have a large particle diameter, e.g., about 15 xcexcm. Also, since it is difficult to have both a coloring material and an ER material (material used for imparting an electrorheological effect to the resin particle) buried in the resin particle, an ER fluid using resin particles has not yet been put to practical use.
Under the circumstances, the present inventors previously proposed a liquid toner composition containing a coloring material and resin particles having such a small particle diameter as 2 to 3 xcexcm of a volume-based median diameter, said composition exhibiting the properties of an ER fluid, and also proposed a method of manufacturing the particular liquid toner composition. As a result of a continued effort to improve further the properties of the ER fluid, the present inventors have arrived at the present invention.
An object of the present invention is to provide a fine particle dispersion exhibiting a high ER effect, the dispersion containing resin particles, which may or may not contain a coloring material, having an average particle diameter controlled to fall within a range of between 0.5 and 20 xcexcm and having inorganic particles attached to or contained in, mainly, the surface region thereof, and a method of manufacturing the same.
According to a first aspect of the present invention, there is provided a fine particle dispersion having resin or both resin and a coloring material dispersed in a carrier liquid, the resin being controlled to have an average particle diameter of 0.5 to 20 xcexcm and having inorganic fine particles attached to or contained in, mainly, a surface layer thereof.
According to a second aspect of the present invention, there is provided a method of manufacturing a fine particle dispersion, comprising the steps of:
fusing under heat and dispersing a thermoplastic resin, which may or may not contain a coloring material, in a solvent having a high temperature dependency in terms of solubility of the thermoplastic resin and having its solubility parameter controlled to control the particle diameter of the particles to be precipitated;
cooling the resin-containing system to precipitate the resin particles, which may or may not contain the coloring material;
adding inorganic fine particles to the system, followed by heating again the system to achieve a sufficient mixing; and
cooling the system to permit the inorganic fine particles to be attached to or contained in, mainly, the surface layer of the resin particles, which may or may not contain the coloring material.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.